Forming filamentary band

ABSTRACT

Band structures comprising a core of parallel filaments and an extruded exterior sheath of thermoplastic organic material and process for their production including the step of compaction of the core by means of a reduced atmospheric pressure.

JEDHDQQ? i 1 [72] Inventor Nigel John Barn [50] Field of Search 1 56/ 180, Harrogate, England 181, 244, 285, 286, 296; 264/172, 174. 176. 257. [21] App]. No. 864,188 88,101,177;117/124,l28.4,140 R,140A.126 [22] Filed Oct. 6, 1969 R, 126 AB, 126 G0, 126 GR. 126 GS. 126 GN; [45] Patented Dec. 14, 1971 161/142144,175.176, 60; 57/144-155, 160-165 [73] Assignee Imperial Chemical Industries Limited London England I References Cited [32] Priority Oct. 16, 1968 UNITED STATES PATENTS 1 g g ggg 3,106,501 10/1963 Cobb et a1. 156/180 [31] FOREIGN PATENTS 933,755 8/1963 Great Britain 161/176 3 [54] FORMING FILAMENTARY BAND 1,006,931 10/1965 Great Britain 264/101 3 6 Claims, No Drawings Primary ExaminerWi1liam A. Powell [52] US. Cl 117/126, AImrney-Cushman, Darby & Cushman 264/88,264/177264/257 ABSTRACT: Band structures compnsmg a core of parallel 51 1 1111. C1 3321 5/12, filaments an extruded exleriorhemh of f w 32 3| 2 game material and process for the1r productlon 1nclud1ng the step of compaction of the core by means of a reduced atmospheric pressure.

FORMING FILAMENTARY BAND This invention relates to band or webbing structures, in particular to structures comprising a core of substantially parallel filaments and an organic thermoplastic sheath and to a process for the production thereof.

Rope structures are known composed of a core of substantially parallel natural fibers or synthetic filaments encased in rubber or synthetic plastics material and a process for the production of such structures having a core of continuous filaments and improved properties has been described in British Pat. No. 1,164,842.

We have now found that the process of British Pat. No. 1,164,842 may be modified to produce band or webbing structures having markedly better properties than such structures heretofore available.

According to the present invention we provide a process for the production of band or webbing structures comprising a core of at least one bundle of substantially parallel filaments said bundles if more than one is present being substantially parallel to one another and an exterior sheath 'of thermoplastic organic material, characterized in that the bundle or assemblage of bundles of filaments arranged as a band of filaments is compacted by passage through a first die and while compacted is subjected to a reduced atmospheric pressure and 'is thereafter extrusion coated with an exterior thermoplastic organic sheath in a second die.

The terms band or webbing as used herein when referring to either a filamentary core or a completed structure according to the invention mean a structure which is appreciably greater in width than in thickness. Such structures being used as belts and similar articles will be of appreciable length compared with their thickness and width. The term band when used to describe the form of a filamentary core includes assemblages of filaments which are continuous or discontinuous across the width of the assemblage as hereinafter further described.

Bands and webbing according to the invention exhibit high tensile strength as the filamentary core wherein the strength resides is untwisted and highly compacted. The high degree of compaction possibly by means of this invention produces a structure having an enhanced stability of cross-sectional shape when bent or flexed.

The term bundle is used herein to denote a group of filaments arranged in parallel fashion. Such a group may be assembled by combining together without twisting a number of filamentary yarns to produce the larger bundle required for a band or webbing or the bundle may be produced directly in the required size as a tow, that is to sayan aligned bundle of parallel filaments having no twist. Filamentary yarns, as normally produced contain a very low amount of twist, referred to as producer twist, which is usually less than 2 turns per inch, and frequently is less than 1 turn per inch, which need not be removed in preparing bundles for construction of a band or webbing.

Any synthetic filament in continuous filament form may be used as the core material and the filaments may be of circular or noncircular cross section or in the form of ribbons. We prefer to use synthetic filaments which have a high extension modulus and preferably also a low extension at break, as for example, polyethylene terephthalate or isotactic polypropylene filaments. Filaments prepared from blends of branched polyethylene and polypropylene or blends of polypropylene and elastomeric olefine copolymers may also be used. Mixtures of synthetic filaments containing a high proportion of filaments which have a high extension modulus may also be used in the process of the present invention. The choice of materials actually used is primarily dependent upon the properties required and the cost of the materials and the mixture chosen may include filaments of lower extension modulus as for example, nylon 6 or nylon 66 filaments. In certain uses fibers having a high density in addition to high strength and extension modulus are required, in which case glass fibers and certain regenerated cellulose fibers are very suitable.

Exemplary of suitable sheathing materials are coatings of low or high density polyethylene or blends thereof, polyvinyl chloride, polyurethanes, polyesters such as polyethylene terephthalate, polyamides such as polyhexamethylene adipamide or stereoregular polypropylene and natural rubber. The sheathing may be of either smooth or ridged external form. It is preferred to use a smooth form of sheathing surface and to have an overall band thickness of less than 10 millimeters. If the sheathing material is subject to degradation by light or other external influences a stabilizing substance or mixture of stabilizing substances may be incorporated in the organic sheathing material before extrusion or the sheathed structure may be treated so as to produce a surface layer of resistant material. Many substances which have a stabilizing action in thermoplastic organic materials are well known, for example ultraviolet light absorbers and phenolic antioxidants in polyolefines, organotin compounds in chlorinated hydrocarbon polymers and carbon black in rubber.

ln producing bands or webbing according to this invention the filaments comprising the core may be arranged in the completed structure as a continuous or discontinuous band across the width of the structure. The latter form of core is preferred for large, wide structures for the penetration of sheathing material through the discontinuities in the core enhances the cross-sectional stability of the final structure to bending and flexing.

Thus according to another aspect of this invention we provide a band or webbing comprising a band as hereinbefore defined of substantially parallel filaments coated with an exterior sheath of thermoplastic organic material.

Extrusion coating machines well known, for example, in the production of electrical cables comprise a hopper containing a supply of thermoplastic coating material, means for supplying this in a molten or thermoplastic state to the surface of the substrate, a compression die to compact the substrate prior to coating and an extrusion coating die. For use in the present in vention such extrusion coating machines must be provided with a means for subjecting the substrate core to a reduced atmospheric pressure during passage of the core through the machine. Frequently it is convenient to provide a compression die and an extrusion coating die in one unit with means for applying the reduced pressure at a point between the dies together with means to supply molten coating material to the coating die. Exemplary of a suitable coating machine are the Pasquetti extrusion coating machine (C. Pasquetti, Varese, Lombardi, Italy) and the Bone coating machine (Bone Bros. Ltd., Alperton, Wembley, Middlesex). in these machines the assembled core is passed into a compression die at the center of which a reduced atmospheric pressure is applied by means of a vacuum pump with its inlet connected to the die at this point. The core is thus subjected to a reduced pressure within the die which is made effective at the input end of the die by the self sealing action of the core filling the die and at the output end by the same action combined with that of the molten sheathing. While still subject to the reduced atmospheric pressure the compacted structure meets an annular flow of molten polymer which is drawn into the core structure and is shrunk thereon by passage of the coated structure within a very short distance into a cooling water bath or jet. When extrusion coating is carried out with the core horizontal it is necessary to maintain it under some tension to prevent drooping until the sheath has solidified.

Bands or webbing produced according to this invention show a much reduced tendency for buckling or disturbance of the sheath, that is alteration of the cross-sectional shape, to occur when a length of the material is compressed axially or bent longitudinally or transversely compared with a structure which has been prepared without the application of vacuum at coating.

Bands or webbing according to this invention may be used in any application requiring a high strength flexible band, as for example as a package strapping wherein one or more lengths of the material is passed around the package and the ends are secured by a clip or by sewing. Bands of the invention have a particular advantage in this use as the ends may be secured by the simple expedient of welding, which should be effected so as to join the core materials in the free ends. Another application in which the high strength and flexibility of the bands of this invention are advantageous is in the reinforcement of large containers, tanks etc. particularly where hoop stresses are large, by using the band to wind about the container and securing the free ends. The following examples illustrate the invention and the manner in which it may be performed.

EXAMPLE I Polyethylene terephthalate yarn having 192 filaments of total denier 1,000, a tenacity of 8.3 grams per denier and a producer twist of 0.75 turns per inch is used as the raw material for preparation of the twistless core, which was single bundle formed by combining without twist 300 ends of the 1,000 denier yarn. The yarn bundle is passed into the compression die of a Bone extrusion coating machine wherein a reduced pressure of 12.5 cm. of mercury is applied to it within the die immediately before coating with molten branched polyethylene (density of polymer 0.919) the temperature of which is 205 C. A 5 cm. wide belt emerged from the die and is cooled with a jet of water before winding up. The belt thickness is 1.5 mm. made up of the core filaments surrounded by a polyethylene coating of 0.7 mm. thickness. The breaking load of the finished belt is 2.4 tons corresponding to a tenacity of 8.l grams per denier.

EXAMPLE 2 A yarn bundle consisting of 70 filamentary yarns as used in example l are passed into the compression die of a Bone extrusion coating machine wherein a reduced pressure of cm. of mercury is applied to it within the die immediately before coating with a molten polyvinyl chloride (B.S.S. softness 4) the temperature of which is 170 C. at the coating head of the machine. A 5 cm. wide belt emerged and is cooled with ajet of water before winding up. The belt has a total weight of 4 Kg./sq.meter, a breaking load of 449 Kg. and a stiffness (measured as hereinafter described) of 1.65 Kg. meters.

EXAMPLE 3 A yarn bundle as used in example 2 is extrusion coated as in that example with a molten polyurethane at a temperature of 170 C. The 5 cm. belt produced has a total weight of 1.8 Kg./sq.meter, a breaking load of 470 Kg. and a stiffness of 0.93 Kg. meters.

EXAMPLE 4 A yarn bundle as used in example 2 is extrusion coated as in that example with a molten branched polyethylene (density 0.919) at a temperature of 205 C. The 5 cm. belt produced has a total weight of L2 Kg./sq.meter, a breaking load of 520 Kg. and a stiffness of 2.4 Kg.cm.

EXAMPLE 5 A yarn bundle consisting of I50 high tenacity rayon filamentary yarns, each of 1,000 denier and a tenacity of 4.5 g. per denier is extrusion coated with branched polyethylene as in example I. The 5 cm. belt produced has a breaking load of 726 Kg. which corresponds to a tenacity of 4.4 g. per denier.

Stiffness of specimens of belt produced in the foregoing examples is measured as follows. A length of the material is laid flat on a horizontal surface with one end slightly overhanging the edge. A weight is attached to the free end and the specimen is pushed slowly further out over the edge until the free end is depressed from the horizontal by an angle of 40. The moment required to produce this depression is calculated and this is the stiffness of the specimen.

lclaim:

l. A process for the production of flexible band structures corn risin bringing together a plurality of continuous synt etlc ilaments romasupply thereofto ormaplurality of small bands of parallel filaments laterally spaced apart to form a larger discontinuous band, compacting each small band by passage through a compression die subjecting the compacted bands to a reduced atmospheric pressure to further compact them and while still subject to the reduced pressure applying a coating of molten thermoplastic organic material about the larger band to form a compact unitary band structure.

2. A process according to claim 1 wherein the exterior sheath comprises low or high density polyethylene, natural rubber, polyvinyl chloride, a polyurethane, a polyester, a polyamide or stereoregular polypropylene.

3. A process according to claim 1 wherein the core material comprises filaments of polyethylene terephthalate, isotactic polypropylene, nylon 6, nylon 66, glass, a blend of polypropylene and polyethylene or a blend of polypropylene and an elastomeric olefine copolymer.

4. A process according to claim 3 wherein the exterior sheath comprises low or high density polyethylene, natural rubber, polyvinyl chloride, a polyurethane, a polyester, a polyamide or stereoregular polypropylene.

5. A process according to claim 4 wherein the polyester is polyethylene terephthalate.

6. A process according to claim 4 wherein the polyamide is hexamethylene adipamide.

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2. A process according to claim 1 wherein the exterior sheath comprises low or high density polyethylene, natural rubber, polyvinyl chloride, a polyurethane, a polyester, a polyamide or stereoregular polypropylene.
 3. A process according to claim 1 wherein the core material comprises filaments of polyethylene terephthalate, isotactic polypropylene, nylon 6, nylon 66, glass, a blend of polypropylene and polyethylene or a blend of polypropylene and an elastomeric olefine copolymer.
 4. A process according to claim 3 wherein the exterior sheath comprises low or high density polyethylene, natural rubber, polyvinyl chloride, a polyurethane, a polyester, a polyamide or stereoregular polypropylene.
 5. A process according to claim 4 wherein the polyester is polyethylene terephthalate.
 6. A process according to claim 4 wherein the polyamide is hexamethylene adipamide. 